Fix an error in the destructor for Shape.cc

core/cross/shape.cc

Index: core/cross/shape.cc
===================================================================
--- core/cross/shape.cc	(revision 194715)
+++ core/cross/shape.cc	(working copy)
@@ -49,9 +49,10 @@
 }
 
 Shape::~Shape() {
+  ElementRefArray copy(elements_.begin(), elements_.end());
   // Unregister any Elements that might think they own us.
-  ElementRefArray::iterator iter, end = elements_.end();
-  for (iter = elements_.begin(); iter != end; ++iter) {
+  ElementRefArray::iterator iter, end = copy.end();
+  for (iter = copy.begin(); iter != end; ++iter) {
     if (iter->Get()) {
       iter->Get()->SetOwner(0);
     }